| 摘要 |
An expanded closed-cell thermoplastic resinous material is made by mixing the thermoplastic resin with a volatile blowing agent, which has a vapour transmission rate through the thermoplastic resin from 0.75 to 6.0 times the transmission rate of the atmosphere into which the mixture is expanded, then expanding the mixture at a heat plastifying temperature and cooling the expanded closed-cell mass. In order to promote the vapour transmission between the expanding agent and the surrounding atmosphere, the expanded material may be retained in the atmosphere at an elevated temperature for a period of time. A mixture of methyl chloride and dichlorofluoromethane containing from 40 to 60% of methyl chloride is specified as a blowing agent. Aliphatic hydrocarbons and perchlorofluorocarbons can also be used as blowing agents. Polymers specified include polymers and copolymers of styrene and substituted styrenes, polymers and copolymers of methyl methacrylate, polymers and copolymers of vinylidene chloride, thermoplastic ester and ether derivatives of cellulose and chlorinated polyolefins. |
